Low loss inductors built-on PECVD intrinsic amorphous silicon for RF integrated circuits

The Q of inductors on Si is limited by the series resistance of the metal at low frequency and the substrate resistivity at high frequency. Oxide is generally used to isolate the useful signal of the inductor from the lossy substrate. However, stoichiometric SiO₂ is processed at high temperature which eliminates the possibility of post-CMOS integration. PECVD amorphous Si can be deposited at low temperature, is easily integrated with most Si-based processes, and intrinsic a-Si:H displays low conductivity. In this work, we show that i-a-Si:H deposited at low temperature (250degC) is used in a novel approach as the isolation material for planar inductors on Si for RFICs. More than 50% improvement in Q was measured when 1.5 mum i-a-Si:H film is deposited on the Si substrate prior to fabricating the inductor. This justifies the influence of i-a-Si:H on the RF performance of an inductor. Intrinsic a-Si: H proves to be a promising material for the isolation of RF devices on low resistivity Si